Recently, there has been interest in converting solar energy into chemical fuels that can be stored, transported, and used when needed. This process occurs in nature through photosynthesis. In artificial photosynthesis, semiconductors are used to capture photon energy and convert it to charge carriers that can perform chemical reactions to make fuels such as hydrogen and oxygen from water, as shown in FIG. 1. Artificial photosynthesis can also be used, for example, to make methanol and oxygen from water and carbon dioxide.